Eddy B. Brixen /
03.01.2005 12:00 PM
Microphones: What to look for

A problem inherent with all microphones is wind noise. Whenever there is any amount of wind or air movement, a wind-noise reduction system, such as the Windjammer from Rycote Microphone Windshields, is necessary.

Handheld microphones

From time to time, you may wonder why microphones look so different. Microphones are special tools, and each one is selected for a specific task. The ultimate microphone does not exist. That is why you will find a huge variety of types from which to choose.

The handheld microphone is an everyday tool for television news journalists. It should work in distances of 5cm to 50cm from the sound source/sources, unlike a singer's microphone, which is always kept close to the mouth.

When selecting a microphone for this job, the first decision to make is which directional characteristic: omnidirectional or a kind of cardioid (unidirectional). One advantages of the omnidirectional is that the tonal balance remains constant and is independent of the distance from the sound source. In addition, it is theoretically (and often in practice) less sensitive to wind and handling noise than a directional microphone.

The advantage of the cardioid is that distant sound sources (like background noise) are attenuated compared to sound sources in the near field (like the voice). On the other hand, the negative side of the same phenomenon (the proximity effect) is a change of timbre with distance.

It is important to choose a microphone having low handling noise as well as low cable-induced noise. Often the transducer is a moving coil type, and it might be sensitive to external electro magnetic fields if not equipped with an additional noise-compensating coil. Low output impedance (<200Ω to 300Ω) and balanced line is, of course, essential. In addition, ON/OFF switches should never be allowed.

To avoid wind noise, an efficient windscreen should be available with high wind reduction and low attenuation of high frequencies. If comparable data is not available (unfortunately, it seldom is), you will have to check it yourself. Remember, the high-frequency level reduction can be significant and has to be compensated for at the editing stage.

Lavalier/miniature/clip microphones

Finally, the microphone should be large enough to leave space for your station logo.

The miniature microphone is a popular choice for television news and drama productions. The microphone is small and can easily be hidden in clothing. In most situations, the microphone will have an omnidirectional characteristic.

Figure 1. Frequency response of a miniature microphone (DPA Microphones’ 4071) designed to retain speech intelligibility when placed on a person’s chest. Click here to see an enlarged diagram.

Due to the typical position on the wearer's chest, the sound field is not ideal. In order to maintain intelligibility of speech, the microphone will need a frequency response that compensates for the loss of consonants. (See Figure 1) This will be provided by a boost of at least 5dB to 10dB around 2kHz to 5kHz.

Remember that only very few ENG mixers include equalizers. Often, time is limited in the edit suite, and necessary frequency corrections may not be carried out. It also pays to check the audibility of cable handling noise.

Normally, the miniature microphone is connected to a wireless transmitter. Remember to get information on how the microphone will work with the chosen transmitter. In some cases, the shielding of the microphone cable is used as the antenna. This may affect the audio signal adversely. Special care has to be taken when using digital wireless systems.

Another important issue is the output voltage of the microphone compared to the input stage signal handling range of the transmitter. In drama production, the voice of the actor can have a wide dynamic range. Furthermore, the audio input sensitivity may differ from brand to brand.

Headset/headband microphones

You should select microphones with many practical fittings and accessories. Efficient windscreens and a variety of fixtures are important. Miniature microphones can be of great help in many situations, if you are able to put it in the right position as a boundary layer microphone.

In sports, the headset/microphone combination is widely used. In television shows, the more discreet headband microphone plays a major role.

Sports commentators on television would normally require a headset with the tightest-fitting ear-cups and the most efficient noise-canceling microphone to overcome the crowd noise. In this application, the appearance does not matter.

Head microphones for television shows should be small in size and suitable for wireless transmitters. A good separation between the pickup zone of microphones is essential. Hence, it is a good idea to choose cardioid microphones for the job, as it is possible to obtain good suppression of background noise from other sound sources on stage. The cardioid microphone should be mounted in a fixed position on the talent's head, as movement may change timbre and pick up handling noise. Especially take care of dangling earrings!

If headbands are to be changed rapidly from person-to-person, it might be appropriate to use the omnidirectional head microphones.

General points for outdoor use

Again, the considerations concerning miniature microphones and wireless systems also apply.

As soon as you bring your microphones outdoors, the weather becomes an issue. Every microphone has a specific sensitivity to wind-induced noise. Every microphone will become useless above a certain wind speed.

Take a close look at how much the windshield will attenuate the wind noise and how much it will attenuate the higher frequencies in the spectrum. Remember, at ground level, the wind speed is in theory zero. Therefore, in many situations, you might be better off with a boundary layer microphone.

Eddy B. Brixen is a consultant with EBB-consult in Denmark.

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